Hi,
     have been tramming our mill and now when we do an automated probe, the mill is not going down exactly in the center of the sensor as it used to. Offset slightly in XY terms

In the interests of keeping things symmetrical and calming the inner OCD, how do I tell Mach3 of the new center for the center of the sensor. The sensor is mounted on the mill table and the spindle approaches it in Z

Have searched a bit on here and google but I don't know enough about Mach3  to understand which posts might be related and which ones are talking about something else completely

Any tips will be appreciated.

I am thinking you must have a probing macro, if so then the offsets will likely need to be changed in it.
Hood

If it's anything like the probing routine I am using then all the info is in the 'Auto Tool Zero' button which is accessed from Operator / Edit Button Script - then click on the Auto tool zero button (which will be flashing).

Save a copy of the script (just in case everything goes pear shaped) and then edit as required to get the correct X -Y position you require.

Tweakie.